LEIGH SALES, PRESENTER: It's a hundred years late, but in time to save the Murray-Darling river system. At least that's the hope of the Environment Minister, who signed the final Basin plan into law today.

Eventually it will return 3,200 billion litres to the system and it'll come into force if it survives 15 parliamentary sitting days.

The Greens will try to strike it down next week, but in this most fractured parliament, the Coalition looks likely to ensure it stands.

And, as political editor Chris Uhlmann reports, that just leaves some more bargaining with the states.

CHRIS UHLMANN, REPORTER: Australia is the driest inhabited continent on Earth, so fights over water hark back to the birth of the nation. When the Constitution was written the country was seared by a decade of drought and power over the rivers was vested in the states.

The biggest brawl was over an East Coast system of 23 river valleys spanning four colonies. The Murray-Darling Basin stretches over a million square kilometres, from north of Roma in Queensland to the mouth of the Murray in South Australia. It's home to more than two million people and grows one-third of the nation's food and along its fragile web of waterways are internationally important wetlands. But 100 years of fractured governance strained the water course. Each state allocated water rights well beyond the capacity of the system. So a century after Federation, another decade-long drought prompted John Howard to attempt a Commonwealth takeover of the Murray-Darling.

JOHN HOWARD, THEN PRIME MINISTER (Jan. 25, 2007): I announce today a $10 billion 10-point plan on a national scale to improve water efficiency.

CHRIS UHLMANN: The incoming Labor government inherited the job and the fight with states, farmers, towns and environmentalists. Its first draft guide for the Murray-Darling recommended allocation cuts of 4,000 billion litres or seven Sydney harbours worth of water. That went up in flames - literally.

OPPONENT OF MURRAY-DARLING BASIN PLAN DRAFT GUIDE: (Kneeling next to bonfire made of copies of the draft guide) That's what it deserves. You bunch of w***ers.

CHRIS UHLMANN: Five years on, the final draft is in and the Environment Minister is optimistic.

TONY BURKE, WATER MINISTER: Australia, a century late, but hopefully just in time, has its first Murray-Darling Basin plan.

CHRIS UHLMANN: The plan's complex, but the theory is simple. The aim is to strike a balance, leaving enough water for a healthy river and taking enough to grow food and support Basin communities. Add it to a separate Commonwealth pledge to spend $1.8 billion on smarter water uses, and in all, an extra 3,200 billion litres will flow back to the environment. But by the time that happens, the Commonwealth will have spent $13 billion on the job and the finish line is a long way off.

TONY BURKE: The entire task isn't finished until 2024 and it's at that point that we've got the volumes that I believe are required to truly ensure that the system is restored to health.

CHRIS UHLMANN: The plan needs the support of the states and SA is on board.

PAUL CAICA, SA ENVIRONMENT MINISTER: We've always said here in SA that we'd base our decision on what the quantity of water required would be on the science that said, "This would be enough water." The science tells us this will be enough.

CHRIS UHLMANN: Queensland farmers believe they can work with what's on offer.

IAN JOHNSON, QLD FARMERS FEDERATION: We've gotta be able to look at the impact more locally and make sure that we can mitigate those impacts in some way. Maybe it's because of the way we do the program, the recovery program or maybe there's some adjustment assistance'll be necessary.

CHRIS UHLMANN: NSW farmers have come a long way towards accepting the plan over the last two years.

ANDREW GREGSON, NSW IRRIGATORS COUNCIL: Whilst the Basin plan was never going to be a good thing, it's starting to look like perhaps the best of a bad lot. So I don't think you'll see the same sort of reaction you did to the guide a few years ago, but still there'll be some discontent.

CHRIS UHLMANN: Commonwealth buybacks of water rights caused a lot of the river community angst. The Environment Minister says that work is largely done, but won't commit to a cap on future purchases and that's looming as the major sticking point for the NSW Government.

ANDREW STONER, NSW DEPUTY PREMIER: But simply put, the Commonwealth has failed on that front. They refused to commit to limits on water buybacks. They refused to provide the evidence, the science to convince us that the water can be obtained through infrastructure measures and not through blunt, simplistic buybacks.

CHRIS UHLMANN: Tony Burke says it's up to the states to nominate alternatives to water buybacks.

TONY BURKE: We've been told by the states that they believes there's about 650 gigalitres worth of projects where they can still meet the environmental outcomes, but do it in a way that's more sensitive to communities. It's up to the states to bring those projects forward.

CHRIS UHLMANN: It's unlikely this dispute will derail the agreement and Victoria's criticism is muted.

TED BAILLIEU, VICTORIAN PREMIER: When you say well we sign it. This is pretty much in the hands of the Parliament now. The states have been a part of the Murray-Darling process.

CHRIS UHLMANN: But there is some heavy fire from environmentalists. Peter Cosier from the Wentworth Group believes the failure to count 1,700 billion litres of groundwater extraction makes all this an expensive exercise in creative accounting.

PETER COSIER, WENTWORTH GROUP OF CONCERNED SCIENTISTS: Now in Australia a rule of thumb is that half the river water comes from groundwater. So if you add 3,200 gigalitres of river water and take away 1,700 gigalitres of groundwater, that'll have a profound effect on the health of the river system itself.

CHRIS UHLMANN: And on cue the Greens stepped up today to say they would move to strike down the plan when it's tabled in Parliament.

CHRISTINE MILNE, GREENS LEADER: The science, the evidence is there. The scientists have come out and said, "If you're serious about saving the Murray, you have to actually guarantee a minimum level of 4,000 gigalitres. You have to actually provide what the river needs," and that's not happening with this plan.

CHRIS UHLMANN: But despite the reservations of some in the National Party, it seems likely the Coalition will back the Government.

SIMON BIRMINGHAM, OPP. WATER SPOKESMAN: We welcome the fact that it's been released and that's important, but as always the devil may well be in the detail. The rhetoric we've heard from Tony Burke today is encouraging. The rhetoric's encouraging. We want to make sure the detail matches and lives up to his rhetoric.

CHRIS UHLMANN: So there is some haggling to go and many years to traverse before the vast array of numbers in this plan are proved in the real world, but the signs for it are encouraging.

Is this the end?

TONY BURKE: There's always been an excuse for delay. Delay ended today. We've now got what we've always needed and what they argued about in the late 19th Century in the Federation debates. We now have a national approach to the Murray-Darling Basin.